1. Field of the Invention
The present invention relates to a magnetic recording medium including a recording layer formed in a concavo-convex pattern, and a magnetic recording and reproduction apparatus.
2. Description of the Related Art
Conventionally, in a magnetic recording medium such as a hard disk, a non-magnetic protective layer is formed over a recording layer in order to protect the recording layer against abrasion caused by contact with a magnetic head and corrosion caused by oxygen and the like in an atmosphere. A lubricating layer is further formed on the protective layer. The protective layer can be formed by a vapor deposition method such as CVD (chemical vapor deposition). The lubricating layer can be formed by dipping or the like.
On the other hand, in the magnetic recording medium, various types of development such as miniaturization of magnetic particles forming the recording layer, change of a material for the magnetic particles, and miniaturization of head processing have been made to largely improve areal density of the recording layer. The improvement of the areal density is expected to continue. However, problems of the limitation of the magnetic head processing, erroneous recording of information onto a track adjacent to a target track caused by broadening of a magnetic field of the recording head, crosstalk during reproduction, and other problems have been made apparent. Therefore, the improvement of the areal density by the conventional development approach has reached the limit. Thus, a magnetic recording medium in which a recording layer is formed in a predetermined concavo-convex pattern, such as a discrete track medium and a patterned medium, has been proposed as a candidate of a magnetic recording medium that can further improve the areal density (see Japanese Patent Laid-Open Publication No. Hei 7-129953, for example).
In the discrete track medium and the patterned medium, it is desirable to fill concave portions of the concavo-convex pattern with a non-magnetic material so as to flatten a surface of the medium from a viewpoint of stable flying of the magnetic head (see Japanese Patent Laid-Open No. 2000-195042, for example). Moreover, it is also preferable in the discrete track medium and the patterned medium to form a protective layer and a lubricating layer over the recording layer in order to protect the recording layer against abrasion caused by contact with the magnetic head and corrosion caused by contact with oxygen and the like in the atmosphere.
However, when the protective layer is formed by CVD or the like, an object to be processed in a shape of a circular disk is held by jigs or the like at several portions, e.g., three portions at an outer circumferential end or an inner circumferential end. Thus, particles forming the protective layer are not sufficiently supplied to a region around the portion held by the jigs. Therefore, the thickness of the protective layer in that region becomes insufficient or no protective layer is formed in that region. Since the outer circumferential end and the inner circumferential end of the magnetic recording medium are usually non-recording regions, corrosion of the recording layer in the region in which the thickness of the protective layer is not enough does not directly cause a problem in recording and reproduction. However, the corrosion of the recording layer may progress from the region in which the thickness of the protective layer is not enough to other regions so as to degrade the recording and reproduction characteristics. Thus, there is a reliability problem.
On the other hand, the protective layer can be deposited on the entire surface of the object to be processed by forming the protective layer to some degree, removing the object to be processed from the jigs, holding the object to be processed again at other portions by the jigs, and further depositing the protective layer. However, the reliability problem remains in this case because the protective layer is thinner around the portions held by the jigs. Moreover, a method is considered which forms the protective layer to be thick on the entire surface of the object to be processed including a recording region in such a manner that the protective layer having a sufficient thickness is surely formed at and around the portions held by the jigs. However, in case of a magnetic recording medium such as a discrete track medium and a patterned medium, for which areal density of 200 Gbpsi or more is expected, a guideline that a magnetic gap between an upper surface of the recording layer and a magnetic head is set to 15 nm or less is issued. Thus, when the protective layer is formed to be excessively thick even by several nanometers, the magnetic gap becomes too large. This may degrade the recording and reproduction characteristics.
Alternatively, as described in Japanese Patent Laid-Open Publication No. 2000-195042, the non-magnetic material with which the concave portions are filled may also be formed on the convex portions and the protective layer may be formed on the non-magnetic material. In this case, the magnetic gap also becomes too large as in the case where the protective layer is formed to be excessively thick, when the non-magnetic material is formed in sufficient thickness at and around the portions held by the jigs. Thus, the recording and reproduction characteristics may be also degraded in this case.